In recent years, lithium ion batteries, nickel hydrogen batteries and other secondary batteries have become increasingly important as vehicle-mounted power supplies or power supplies of personal computers and other portable terminals. In particular, lithium ion batteries, which are lightweight and allow the obtaining of a high energy density, are expected to be preferably used as vehicle-mounted, high-output power supplies. In this type of battery, a battery structure is known that is provided with a wound electrode body in which a sheet-like positive electrode and a sheet-like negative electrode are laminated and wound with a separator.
However, in this type of battery, it is necessary to produce the electrode body and the battery case (namely, the external container) separately followed by housing the electrode body in the battery case. Metal packages are frequently used for the battery case, and in such cases, it is necessary to package the electrode body in an insulating film to insulate the metal package from the electrode body. For example, Patent Document 1 discloses a configuration of a secondary battery in which an electrode group is inserted into an insulating member in which a polyimide thin film having a thickness of 50 μm is formed into a bag shape to electrically insulate the electrode group from a battery case. Furthermore, another example of a patent document is Patent Document 2.
Patent Document 1: Japanese Patent Application Laid-open No. 2003-59537
Patent Document 2: Japanese Patent Application Laid-open No. 2003-7340
However, when the periphery of an electrode group is covered by an insulating member in the shape of a bag as described in Patent Document 1, an electrolyte solution is unable to pass through insulating member when injecting electrolyte solution, thereby resulting in the risk of impairing permeation of the electrolyte solution into the electrode group. As a result, uneven permeation into the electrode group occurs easily. In addition, since convection flow of electrolyte solution is impaired by the insulating member, a long period of time is required for the electrolyte solution to permeate into the entire electrode group, thereby resulting in the risk of poor battery productivity.